The trend in integrated circuits is toward higher performance, higher speed and lower cost. Correspondingly, device dimensions and element sizes are shrinking and gate dielectrics must scale accordingly. As physical gate dielectric thickness has decreased, the need for a higher dielectric constant and less leaky gate dielectric has arisen. In advanced metal oxide semiconductor field effect transistors (MOSFETs) silicon oxynitride (SiOxNy) layers are used as a gate dielectric. MOSFET transistors include a channel region formed in a silicon substrate, an N or P doped polysilicon gate formed on top of a thin gate dielectric layer and aligned over the channel region, and source/drain regions formed in the silicon substrate on either side of the channel region.
However, a problem with SiOxNy gate dielectrics is thickness and nitrogen concentration variation across the wafer. Across wafer thickness and nitrogen concentration variation of the gate dielectric leads directly to across wafer threshold voltage variation, especially in P-channel field effect transistors (PFETs), causing variations in performance of individual integrated circuit chips from the same wafer. Therefore, there is a need for a method of fabricating a SiOxNy layer having a relatively uniform across wafer thickness and nitrogen concentration.